This invention is an improvement in the composition of the membrane disclosed in applicant's U.S. Pat. No. 3,659,615 issued May 2, 1972, comprising a silicone and a wax as an encapsulation composition for an electronic heart pacer.
It is well known that silicones including silicone rubber are non-reactive to the fluids of the body, repell water, and have endurance at high and low temperatures, however, they have been found to be permeable to electrolytes and their ions which are detrimental to the electronic components in which the silicone is the encapsulating material. Also temperature vulcanized silicones for encapsulating electronic components in situ often cannot be used because to heat vulcanize or polymerize such silicones would be detrimental to the electronic components encapsulated by them. On the other hand, room temperature vulcanized silicones exhibit greater water vapor penetration, are soft, have poor abrasive resistance, and are generally weaker than heat vulcanized silicones. Thus the permeability of these silicone compositions is materially reduced by the incorporation therein of a wax to fill their pores, and particularly beeswax. However this wax did not strengthen or toughen the composition any. Therefore, in order to improve their resistance to chemical decomposition, polytetrafluoroethylene was added to these silicone compositions, since it was well known that polytetrafluoroethylene increases the chemical resistance and strength of silicones.